Gas accumulators, such as floating piston accumulators, diaphragm accumulators and bubble accumulators, have a preadjustable pressure set point before their attachment to the fluid circuit on the gas side. This point is also termed the initial gas pressure of the accumulator.
Such accumulators now need to control the initial gas pressure required for the operation as authorized, at certain time intervals, since certain gas losses are to be calculated dependent upon the method of operation of the accumulator. Until this time, for this purpose, the fluid circuit and the attached accumulator are conventionally made pressureless. At least the part of the assembly relating to the accumulator is made pressureless to check the pressure set point and/or the initial gas pressure of the gas found in the accumulator in this pressureless state, and if necessary, to replenish it. The gas is mostly in the form of nitrogen gas. A filling and checking device is mounted on the gas side of the accumulator for carrying out this known method. The actual pressure level prevailing on the gas side is measured by means of a manometer. If this actual pressure falls below the level of the initial gas pressure, the accumulator is filled by means of the filling device. This filling process is monitored by the manometer. The resulting processing method is time-consuming. Alternatively, the accumulator, together with the component part of the fluid circuit, is then not ready for work.
In a method of this sort for measurement of the pressure of a gas in a gas accumulator according to JP-A-1-73232, a pressure measurement curve is formed over a time period. Initially, in the time period the liquid pressure rises very sharply in a straight line, and then changes over, with increasing measuring time, into a smoothly rising curve. At the point of changing over from the linear to the curved pressure measurement pattern, the gas pressure in the bubble accumulator corresponds precisely to the fluid pressure measured at this point. To shorten the measuring time in the known method, it is suggested to undertake a measurement only in the time interval or within that "window" in which according to the process the aforementioned break in the measurement curve is expected. A comparable method is disclosed by JP-A-1-54325, whereby the relevant measurement is performed by means of a cyclical measuring device at predetermined uniform time intervals.
By this automatic or manual detection method for the measurement of gas, occurrences of gas losses can be determined for the hydropneumatic accumulator. However, upon detection of gas pressure outside the preadjusted measured value range in the form of the "window", this known method of measurement cannot determine whether actual gas losses have occurred and/or whether an accumulator defect is present and/or whether the measuring device does not work reliably. To overcome this drawback inherent in the known method, it is possible basically to carry out a complete measuring cycle (longer than 20 seconds) and finally to evaluate the measured curve. Generally speaking, a computer is then absolutely required. A rapid disconnection, for instance within safety/security ranges, such as in nuclear power plants or the like, of the fluid circuit associated to the relevant gas accumulator is then however no longer guaranteed whatsoever.